Submitted by: Patel shivam

1. INTRODUCTION

International of mcompetition in machine tool manufacture demands flexibility, high quality, reaction to the market demands and low costs. Therefore the processes and machines are designed with modular structure. A main spindle box could be such a module achine tool.

The most important factor affecting machining accuracy is an accuracy of the machine tool itself resulting from low stiffness and damping ratio of machine tool structure. In this paperthe feasibility of applying new material is studied in order to improve static and dynamicperformances of the structure to desire level. The new design of a main spindle box structure is made of polymer concrete instead of cast iron structure [1, 2, 3].

Polymer concrete consists of a mineral filler and a polymer binder. When sand is used as filler, the composite is referred to as a polymer concrete. Generally, any dry, non-absorbent, solid material can be used as filler [1, 2, 3].

The sand and the fillers are cheap and natural materials available for easy use. The overall process of production of polymer concrete is performed on room temperature and recycling of the materials is much easier than cast iron. Also, the control of the properties of polymer concrete may be much easier and less costly in comparison with cast iron. As a results of the above and some other advantages (flexibility of the design, short development time, simple and less costly production process) the overall competitive advantages of the company may significantly improve [1].

Table 1. General Characteristics of Constructive Materials

2. REDESIGN OF SPINDLE BOX WITH POLYMER CONCRETE

The aim of this investigation is the possibilities of use of polymer concrete in buildingmachine tools structures. For that purpose, the NC lathe Mazak QT 10 headstock’s housing is completely redesigned and polymer concrete constructive material has been chosen and applied.

The available references [1, 2, 3] have shown same examples of use of polymer concrete in substitution of cast iron in the design of machine tool beds. We have decided to investigate the possibilities of the use of polymer concrete in main spindle housing design due to the more demanding requirements connected with the dissipation of temperature, damping and high accuracy of the structure. To be able to redesign the original housing for the purpose of material substitution, we have performed static, dynamic and thermal analysis of the structure.

The differences in the material properties (table 1) have initiated an iterative process of redesign with the aim to achieve properties of the original design. Both models, of original and redesigned housing are shown on figure 1.

a. Original b. Redesigned Figure 1. Models of main spindle housing

3. THEORETICAL AND EXPERIMENTAL STUDY OF NEW DESIGN

We have performed wide numerical and experimental investigations of static, dynamic andthermal behaviour of original and redesigned housing, part of which are presented in this article .

3.1. Statical Modelling and Analysis

Modelling and processing of housing were performed with the use of ALGOR and I-DEAS commercial packages [1]. Figure 2 shows maximal principal stresses of both models. Comparative analyses of the statical characteristics (displacements, Von Mises, Maximal Principal Stress, Mass and Young’s module) of both housings (original and redesigned) are shown on figure 3. Despite worsening of Von Mises and maximal Principal Stress the new design satisfied the limits. We have reduction of mass of redesigned housing for approximately 50% in comparison with the original design which strongly recommend the useof polymer concrete [1].

a. Original b. Redesigned

Figure 2: Maximal Principal Stress of Models

3.2 Dynamical Modelling and Analysis

We have used the same models, developed with ALGOR and I-DEAS, for dynamic analysis of both housings [1]. The comparative analysis of Eugene frequencies of both models is shown in figure 4. As we can see the Eugene frequencies of polymer concrete design are twice higher then those of cast iron design which represents certain improvement of the design. Figure 5 shown comparative analysis of the experimental data of the damping ratio of both designs. The results show superior performances of polymer concrete housing incomparison with cast iron structure [1].

Figure 3. Comparative Analysis of Statical Characteristics

Figure 4. Comparative Analysis of Dynamical Characteristics

Figure 5. Comparative Analysis of Experimental Damping Ratio

While two types of aggregate, ocean sand and Sierra Nevada pea gravel, are fed into the hopper of the mixer, a pipe mixer adds blended polyester resin. A screw-type auger thoroughly mixes these materials then feeds them into the slip form paver for placement.

After placing the overlay, workers use a nuclear density tester to test its compaction and density. Compaction on this job averaged 99% to 100% of the standard, exceeding the minimum specifications of 97%. The overlay also was tested for polyester resin content. Results showed a content of about 11.05%.

Before choosing a resin binder, check its specifications carefully. A good binder should have:

• A low viscosity so it’s easy to mix, place, and finish (viscosity can be varied somewhat to accommodate different applications methods)• A 15- to 45-minute gel time to give workers enough time to place and finish the overlay before it cures• No solvents or ingredients that can evaporate during curing and cause shrinkage cracking• A minimum bond strength to concrete of 250 psi• A compressive strength capability of more than 5000 psi• A tensile elongation of at least 30% and a tensile strength of more than 2000 psi (both indicate good flexibility and resilience) Resin binders having these physical properties can produce polymer concrete overlays with life expectancies of 20 years or more if the overlays are properly installed

Mixing polymer concrete Poor-quality polymer concrete overlays often are the result of inaccurate

proportioning and inadequate mixing of the binder components and aggregate. Mixing the binder components at the ratios specified by the supplier is critical. Once the components are mixed they start a chemical reaction that continues until the polymer concrete hardens. Any variation of the mixing ratios can result in a soft, uncured overlay. Thorough mixing of the binder components also is important. Failure to mix the components completely can result in a non uniform overlay with soft and hard areas.

If the premixed method of overlay placement is used (described below), aggregate must be added to the mixed polymer binder. Again, attention to specified mix ratios and thorough mixing are necessary to ensure uniformity. Polymer concrete components can be batch-mixed in a convention a concrete or mortar mixer.

However, better quality control is possible by using a machine that automatically proportions, mixes, and dispenses components. This ensures mixing accuracy and eliminates batch-to-batch inconsistencies.

The machine should be carefully calibrated and the calibrations should be checked frequently during machine use.

Installation methods

Two methods are generally used to apply polymer concrete overlays:Premixed or slurry method—In this method, the binder components and aggregate are premixed to form a polymer concrete which is then spread over the deck at the required thickness. The mixture should contain an ll% to 14% resin content based on aggregate weight. Using a trowel, bull float, or vibrating screed, apply the mixture over the primed deck surface to meet specifications for compaction ,surface profile, and finish.

Use screed rails to establish a specified minimum application thickness.Because polymer concrete has rheological properties different from portland cement concrete, finishing tools may have to be modified somewhat to better handlepolymer concrete. Mechanical screeds designed to place polymerconcrete are available.

Immediately after placing the overlay, broadcast additional aggregateonto it at a rate of about 2 pounds per square yard or until no wet spots are visible. The aggregate adheres to the wet binder, forming a nonskid surface. Sweep away any un bonded aggregate after the overlay cures.

Curing

A polymer concrete overlay cures much faster than a conventional portlandcement concrete overlay. But if polymer concrete isn’t allowed to cure sufficiently before the overlay is opened to traffic, damage can result. Curing time varies depending on temperature conditions and type of polymer used. Generally, the warmer the ambient temperature, the shorter the cure time. At 95° F, the overlay is ready to accept vehicle traffic in 1 to 3 hours; at 75° F, 2 to 6 hours is required.

An easy way to test for sufficient curing is to poke the overlay with a screwd river. If the screwd river doesn’t leave a mark, the overlay is probably ready fortraffic. However, have the project engineer or a representative of the resin binder supplier confirm overlay readiness before reopening the bridge deck.

Proven performance

Investigation into the use of polymers for preparing polymer concreteand mortars began more than 30 years ago. But early attempts at using polymers for bridge deck overlays met with limited success due to problems with materialproperties and mixing and installation methods.

Most of these problems have been solved. In fact, the U.S. Department of Transportation removed some polymer concrete systems from its list of experimentalmaterials in 1989. Now repair and rehabilitation projects using these systems may be eligible for full federal funding. Technological advances in polymer materials have improved their flexibility and their chemical compatibility with concrete, resulting inoverlays that are more durable and more resistant to shrinkage and cracking. Mixing and application procedures have improved too, and equipment is now available to speed these procedures and improve acc uracy.

Because of these advances, an increasing number of polymer concrete overlays have been installed in the past 10 years in the United States and Canada. Transportation departments are monitoring the performance of many of these overlays and reports indicate that the overlays are performing well

Machine Mixing Instructions

The mixture is obtained by adding water into a clean container and then gradually adding the powder. Add approximately 1 gallon of water for each 50 lb bag of Polymer Concrete Patcher to be used. If the mortar becomes too difficult to mix, add additional water until the desired consistency is achieved. The mixing process can be performed in a cement mixer or in a bucket (working manually or with a mechanical agitator) or using a continuous mixer until homogeneous, lump-free mixture is obtained. It is also possible to use a sprayer to mix and simultaneously pump the mixture, using a rotor/ stator system suitable for the granulometric gradation of the mixture.

Hand Mixing Instructions

Empty the bags into a suitable mixing container. Add approximately 1 gallon of water for each 50 lb bag of Polymer Concrete Patcher to be used. Work the mix with the necessary tools, and add additional water as needed until the desired consistency is achieved. Make sure all the material is adequately wet before proceeding with the application.

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