On the Choice of Chip Thickness Based on the Multiplicity of Load Variation on the Cutting Chain
Abstract Generated abstract
This paper examines how chip thickness affects the nonuniform loading of the cutting chain drive in bar-type earth-cutting machines operating in frozen soils. Using experimental relationships between the load-variation factor, defined as the ratio of maximum to average torque on the drive-sprocket shaft, and chip thickness under different cutting speeds, feed speeds, soil types, and chain designs, the authors compare loading behavior for sand and sandy loam. The results indicate that increasing chip thickness generally reduces load variation, with especially high dynamic loads occurring in frozen sandy loam at small chip thicknesses. The paper concludes that, to keep the load-variation factor within about 2 to 3, cutting regimes should be selected to provide chip thicknesses of at least 8 to 10 mm for both slatted and unsupported chains.
Full Text
ON SELECTING CHIP THICKNESS BASED ON THE LOAD VARIATION FACTOR ON THE CUTTING CHAIN
I. G. Basov, F. F. Zelinger, B. L. Stepanov
(Presented by the Department of Mining Machines, Mine Transport, and Mining Mechanics)
The chain working member of a bar-type earth-cutting machine, in the process of cutting frozen soil, experiences a nonuniform load over time. This occurs as a result of the periodic change in the instantaneous winding radius of the chain on the driving sprocket and in the number of chain teeth in contact with the medium being excavated. In addition, when the next chain hinge encounters a sprocket tooth, and when the cutter encounters hard inclusions in the soil mass, periodic sharp impacts occur in the cutting chain.
Thus, when designing bar-type earth-cutting machines it is important to know not only the magnitude of the torques arising in the transmission of the cutting-chain drive, but also the nature of the nonuniformity of loading, the multiplicity, and the number of load oscillations.
The magnitude of the loads depends on the cutting and feed speeds, as well as on the thickness of the chip removed by the bar cutters. Of considerable interest is the study of the nature of the load-variation factor \(\left(\text{the ratio } \dfrac{M_{\max}}{M_{\text{av}}}\right)\), arising on the shaft of the driving sprocket of the cutting chain, as a function of chip thickness.
As a result of experiments [1], it was established that the load-variation factor of the shaft of the driving sprocket of the cutting chain fluctuates over wide limits depending on the operating regime of the working member (Fig. 1, \(a, b, c\)).
The general pattern is that, with an increase in the thickness of the chip removed by a tooth of the cutting chain, the ratio \(\dfrac{M_{\max}}{M_{\text{av}}}\) decreases—at first intensively, and then only slightly. The same value of the ratio \(\dfrac{M_{\max}}{M_{\text{av}}}\) corresponds to different chip thicknesses for different feed speeds \(v_{\text{f}}\). With an increase in the cutting speed \(v_{\text{c}}\), the load-variation factor at \(v_{\text{f}}=\text{const}\) increases, but it will be the smaller the greater \(v_{\text{f}}\) is. The load-variation factor, when cutting sand with a freezing depth of 2 m using unsupported (“Ural-33”) and slatted (KMP) chains, is practically the same for equal chip thicknesses (Fig. 1, \(a, b\)). Hence
it follows that, for equal \(v_{\mathrm{p}}\) and \(v_{\mathrm{pl}}\), the ratio \(\dfrac{M_{\max}}{M_{\mathrm{avg}}}\) will be somewhat larger for the barless chain.
Cutting sandy loam with a frost depth of 1.5 m by a single-bar chain is accompanied by large dynamic loads (Fig. 1, c). A particularly significant multiplicity of moments is observed at chip thicknesses from 1 to 6 mm. At a slot-cutting speed in sandy loam of up to
Fig. 1. Dependence of the multiplicity of change in the load on the drive-sprocket shaft of the cutting chain on chip thickness during cutting:
a—sand with a frost depth of 2 m by a KMP chain; b—the same, by a “Ural-33” chain; c—sandy loam with a frost depth of 1.5 m by a KMP chain. Depth of the slot being cut, 1.5 m. Feed rate: 1—13.5 m/h; 2—20.6 m/h; 3—30 m/h; 4—64.6 m/h; 5—18.8 m/h; 6—33 m/h; 7—80 m/h; 8—100 m/h.
33 m/h, the ratio of the maximum value of the moment to the mean is 9.2–9.3, which is three times greater than when cutting sand with bar and barless chains at the same slot-cutting speed and at the same chip thickness.
For slot-cutting speeds of 18.8–33 m/h, the smallest multiplicity of moments corresponds to a chip thickness of 10–20 mm.
It follows from the above that, in order to obtain a multiplicity of load variation in the cutting-chain transmission of no more than 2–3, it is necessary to select cutting speeds in such combinations that ensure
chip thicknesses removed by the cutters are not less than 8–10 mm. This requirement must be met when cutting frozen soils of various mechanical strengths with both slatted and slatless chains.
REFERENCES
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O. D. Alimov, I. G. Basov, F. F. Zelinger, “Experimental study of cutting regimes for frozen soils with a trenching excavator.” Construction and Road-Building Machines, No. 9, 1965.
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V. A. Brenner, D. M. Lyuboshinskii, I. S. Zilbert, A. P. Dumchev, V. I. Efremov. “Investigation of the process of nonuniformity in coal breaking.” Coal and Mining Machinery. Issue 10, NIIINFORMTYAZHMASH, Moscow, 1965.