The various machines produced in our conmpany, like cement grinding,raw material grinding, coal grinding, adopt edge-transmission if the diameter is no more than Φ3.8m. The operating principle is that the engagement between large gear and small one drives cylinder of grinding machine.The large gear has to be big enough to meet the requirements due to the cylinder diameter ,rotating speed and way of assembling.And it has a complex stucture. In order to ensure engagement precision, work stably and evenly ,as well as keep load uniformly distributed,it is quite important to determine how to machine it. Let’s take the large gear used in coal grinding Φ3.8×7.25+3.5m for instance and make a analysis to its machining procedure.
二、The large gear structure and process datum
The large gear used for grinding machine with the size of Φ3.8×7.25+3.5m, material ZG310-570, precision level 9-9-8-JM（GB10095-88）,technical data: Z=206，m=28,α=20°, Tooth depth coefficients h*=1, modification coefficient x=2.8, addendum circle diameter: da=5963.76mm。For dimention and tolerance , see DWG 1
Process datum:According to tolerance and assembling of large gear, its datum diameter should beΦ 4345(female end), The position of reference surface B,C,A will affect position accuracy of hole 48-Φ52, which lead to affect installation precision of large gear, if so, the cylinder of grinding machine cannot work pretty well.
三、The machining procedure：
The large gear is kind of big cast steel with enough margin. Because of two halves that assemble as one,the every half of the cast steel is easily deformed.In order to ensure the machining margin , the scrape is nessessory. The scrape can keep a good connection between the two halves,and it can also check whether the margin is enough or not. According to the existing scrape on the end face, keep the two halves of cast steel in the right position during assembling them as one. And then boring connention holes and pin holes , fasten the two halves with bolts. Machining inner and outer circle as well as various end faces by vertical lathe. The lathing here is one of the most important procedure. To ensure all the dimensions and tolerances and keep the product undeformed in the couse of lathing as per drawing, machine it as follows:
1.Keep the more flat end face of the blank as datum, put it on the trim plate , and make it on the right position according to the existing scrape on the surface of the product, then clamp it tightly(See DWG 2). Rough-lathe all the parts of the product as much as possible, keep margin for 5mm, then reverse end for end , Rough-lathe the rest of the product, keep margin for 5mm.
2.Remove the product from the lathe, put it on the platform, loosen the bolts, make it deformed for 24 hours in a natural way (or vibration failure for over 2 hours). That is to release the inner stress caused after rough machining.[/caption]
3.Re-fasten the bolts and pins firmly.
Place the product flatwise on the trim plates with same high, clamp inner circle of Φ5700 (See DWG 3)
4.Make the product on the right position in accordance of machined surfaces, and the clamp force does not have to be too strong lest it would be deformed.
5.Fine-lathe various parts of the product as per drawing, scrape pitch circle with the tip of lathe tool, then machine female end of Φ4345. The inner hole and end face can be seen as reference for assembling .
6.Reverse end for end, clamp as showed on the DWG 3, fine lathe the rest of product as per requirement showed on the drawing.
After lathing, the tooth can be machined. To ensure the accuracy of the tooth, decrease the load of the lathe and prolong the life service of the lathe, the product can be machined by two different machines.
1.First, scrape the outline of the tooth,the scrape should be on the non-reference surface,then clamp the product on the gear milling machine, rough milling the tooth with fonger-shaped milling tool. Keep margin 2-3mm for each side, and keep the margin even.
2.After rough tooth milling, clamp the product on the Φ8m gear hobbing machine,and then fine-hobbling the tooth in two runs till it meets the requirement of the drawing.
After the tooth is completed, scrape and drill holes and thread holes,but the holes of 4-Φ50H7 should be drilled upon assembly with flange holes on the cylinder.Therefore drill the holes to 8-Φ42 first , then assemble cylinder together, drill them at once in accordance with drawing.
Last, take the large gear apart in two , fasten them with tightening device,that will be convenient for transportation.
It is imperative to prepare a machining procedure according to the reference surface when setting a rule of machining for large cast steels, especially for the large gears used in grinding machines.Meanwhile , the deformation should be taken into consideration during machining.
It is ,therefore,nessessory to increase the frequency of the product clamping. If the margin is too much,the rough-milling should be carried out before fine-milling.That can decrease the load of the milling chanchine,increase the life service of the machine.